1. Field of the Invention
The invention relates to methods and apparatuses for delivering materials having liquid and solid constituents such as salt and clay slurries. The invention has particular applicability for hauling sodium chlorate and its precursor salts.
2. Description of the Related Art
Many industrial processes employ large quantities of slurries, such as solutions. By way of example only, in a paper manufacturing process, large quantities of sodium chlorate are used as a bleaching agent. Sodium chlorate is typically manufactured from granular sodium at a sodium chlorate plant. Usually, granules are delivered to the chlorate plant in dump trucks, and are dumped into mixing pits near the plant. Water is then added to the pits, and the contents of the pits are mixed to form a slurry before being pumped off to the sodium chlorate plant. This process is not only time consuming, but also labor intensive.
Alternatively, the slurry may be pre-made and delivered in tanker trailers to the sodium chlorate plant. This approach is costly and inefficient since the heaviest component of the slurry is water. In effect, the shipper is required to pay freight for essentially hauling water. And due to the weight of water, a mobile tanker might easily exceed government imposed weight restrictions before the tanker is completely full, leading to further inefficiency.
After sodium chlorate is manufactured, it may be transported to a paper mill as a slurry. However, since sodium chlorate slurry may be appropriately 55% water by weight, doing so is costly and efficient for the reasons discussed earlier.
Due to the expense and inefficiency of transporting slurries, some shippers have resorted to hauling powdered sodium chlorate in rail cars and then adding water at the paper mill using a sparger system.
With a sparger system, a pump, external to the rail car, conveys water into the rail car while another pump conveys a mixture of liquid and solid from the rail car to an external mixing tank. Sparger systems do not typically employ any mechanical agitation in the tank. Rather, a sparger system continuously swaps the contents of the mixing tank and the rail car in an attempt to place all of the sodium chlorate into slurry form. There are a number of draw backs with sparger systems. First, they are time consuming to use. It typically takes about one half of a work day to turn a single rail car of dry sodium chlorate into slurry form. Second, sparger systems are typically not fully effective. Sometimes as much as 10 percent of a sodium chlorate load will not become slurry and will cake on the bottom of the mobile tank in which it is transported. In addition, the sparger system requires external equipment and excessive labor.